The effect of the VOF-CSF static contact angle boundary condition on the dynamics of sliding and bouncing elliposidal bubbles.

Abstract

The staticcontactangle is the only empiricism introduced in a Volume of Fluid?Continuum Surface Force (VOF?CSF) model of bubbly flow. Although it has previously been shown to have a relatively limited effect on the accuracy of velocity and shape predictions in the case of large gas bubblessliding under inclined walls (e.g. Cook and Behnia, 2001), it may have a more determining influence on the numerical prediction of the dynamics of smaller ellipsoidalbubbles which were shown by Tsao and Koch (1997) to bounce repeatedly when sliding under inclined walls at certain wall inclinations. The present paper reports on the influence of surface tension and the staticcontactangle on the dynamics of an ellipsoidal air bubble of equivalent diameter De = 3.4 mm. The bubble Eotvos and Morton numbers are Eo = 1.56 and Mo = 2 ? 10?11 respectively. The computational results are achieved with a Piecewise Linear Construction (PLIC) of the interface and are reviewed with reference to experimental measurements of bubble velocity and interface shape oscillations recorded using a high speed digital camera. Tests are performed at plate inclination angles? ? {10?, 20?, 30?, 45?} to the horizontal and computational models consider three staticcontactangles?c ? {10?, 20?, 30?}. The staticcontactangle has been found to have a significant effect on the bubbledynamics but to varying degree depending on the plate inclination. It is shown to promote lift off and bouncing when the plate inclination angle reaches 30? in a way that does not necessarily reflect experimental observations.